A Research On Regularity Of Coalbed Methane Enrichment In Zhengzhuang Block

The coalbed methane field of Qinshui Basin is located in the southeastern part of Shanxi Province. It is an important source of the Huabei Oilfield which has stable, high-speed growth of oil and gas equivalent.After exploration and practice of coalbed methane field in recent years, Huabei Oilfield has some success, but also has some problems. It has a complex geological conditions, the thick coal reservoir, cracks heterogeneity in southern Qinshui basin and difficult exploration and development of CBM. The lower production and higher costs of average per well are due to a lack of understanding of the law of coalbed methane enrichment, restricting the rapid and efficient development of coalbed methane business. It can not meet the needs of the coalbed methane exploration if we copy conventional oil and gas geophysical exploration and well logging technology. So we need to form a series of specialized acquisition for the Qinshui Basin geological features containing collection, processing, interpretation, prediction as one of the coalbed methane-rich regional geophysical comprehensive evaluation supporting technology, so as to speed up the pace of CBM exploration and improve development efficiency.Taking the Zhengzhuang block for example, the research in this paper mainly follows aspects of the comprehensive evaluation of the coalbed methane-rich region and gains some understanding for the difficult problems:1. Geological featuresThe Qinshui Basin is a typical North China sedimentary, the basin structure formation is mainly the Yanshan Movement. The stratigraphic drilling from top to bottom as follows:Cenozoic Fourth(Q), the Mesozoic Triassic (T), Permian (P), Upper Paleozoic Carboniferous (C), Lower Paleozoic Ordovician(O). Shanxi Formation is lakes and rivers swamp deposits and Taiyuan Formation is paralic deposition. The main gas source layer group is on the No.3coal of Shanxi Formation and No.15th coal of Taiyuan Formation. It has a large thickness and high gas in the coal seam. The active groundwater conditions in the region prone to collapse column, which is unfavorable for the seam preservation.2. The structure of coal rockThrough the analysis of the differences in the physical properties of tectonic coal, partings, the original bituminous coal and its different response characteristics on logs, coal rock structure is identified and divided, which we understand the law of distribution of coal rock, it plays an active role in avoiding drilling risk and doing rational exploitation.3. Fine interpretation of the seismicStarting from the source of seismic data, collection and processing techniques and methods are chosen in the Qinshui basin coalbed methane, it provides data protection for fine interpretation. In the explaining process, using coherent body and three instantaneous attribute effective identification of small faults and collapse columns; to complex surface conditions and underground speed changes in the adverse conditions, using the space variable speed technology, the establishment of a high-precision three-dimensional velocity field, doing time-depth conversion, the drilling correction and real reflecting the seam depth, it is fine portrayed to implement the seam slightly fold structure, to create the conditions for the establishment of a three-dimensional geological model; using seam curvature properties to predict the direction and distribution of coal seam cracks.After the study, it is found that Zhengzhuang block as a whole is a North tilting wide and gentle slopes, gentle strata, which mainly growing two large waist fault of Sitou and Houchengyao, the development of small faults majoring in north east direction, which has a tectonic pattern of "north-south zoning, interlacing concave-convex from east to west", the collapse column is mainly the half column, which diameter100-300m, it mainly due to constantly scouring action of the groundwater, the collapse of the Ordovician limestone fall of the formation along the fault strike was characteristics of banded concentrated.4. Coal reservoir predictionAs researched Qinshui CBM reservoir conditions, it is believed that the master factors of affecting the CBM reservoir are:seam depth, seam thickness, coal rock thermal evolution, the reservoir properties, structural conditions, the rock closed conditions, hydrodynamic conditions, collapse columns. The comparative analysis of well logs in the region to draw seam survey response characteristics of the three high and two low, which are high resistivity, high compensated neutron high acoustic travel time and low natural gamma, low-density. To do this, selecting the appropriate logging curves and prediction methods of coal seam thickness, seam micro fractures containing gas commenced seismic inversion prediction which reasonably predict high gas zone, providing a basis for evaluation of coalbed methane-rich region preferably.5. The law of coalbed methane enrichmentCBM as an unconventional gas reservoir, the accumulation process by the coal seam itself, the upper and lower strata and around the combined effect of a variety of geological processes, has its special accumulation conditions and control system. By fine structural interpretation, variable velocity mapping, attributes analysis techniques, logging evaluation techniques and reservoir prediction technology of advanced seismic geophysical technology and methods, researched the results in Zhengzhuang applications relationship between coalbed methane gas and the master controlling factors of CBM to identify which law optimized deployment recommend, to provide protection for the choice of the high-yield area for coalbed methane enrichment.Currently, the set of technologies and methods in the process of research have been widely used and achieved good results, it can more accurately predict coalbed methane yield rich region, providing a reliable geological basis for the deployment and development of coalbed methane drilling program, providing technical supports and theoretical basis for research and production.